The present invention relates to a method of manufacturing a silicon single crystal and an apparatus for pulling a silicon single crystal, and more particularly, to a method for supplying a voltage to detect leakage of a silicon melt or touch of a seed crystal at the silicon melt. Also, the present invention relates to a vitreous silica crucible, which employs the method for supplying a voltage and is used for pulling a silicon single crystal.
As one of manufacturing methods of a silicon single crystal for semiconductor devices, Czochralski method (CZ method, hereinafter) is well known. In CZ method, a seed crystal is dipped into a silicon melt obtained by melting silicon raw material in a vitreous silica crucible, and a silicon single crystal grows by gradually pulling up the seed crystal while rotating the crucible and the seed crystal relatively to each other. To manufacture a high-purity silicon single crystal for semiconductor devices, it is required that the silicon single crystal should not be contaminated due to dissolution of impurities contained in the vitreous silica crucible, and the vitreous silica crucible should also have a heat resistance enough to be endurable during pulling for a long time.
Also, in the manufacturing of silicon single crystals, it is an important issue to secure the safety during work for a long time. For example, in Patent Document 1, a method of detecting leakage of a silicon melt in a silicon single crystal pulling apparatus is disclosed. This technique is, in an apparatus having a conductive supporting means supporting a vitreous silica crucible and a conductive suspender suspending a seed crystal, to detect leakage of a silicon melt by supplying a constant voltage between the supporting means and the suspender and by detecting change in the electric current flowing between the supporting means and the suspender. Also, in patent document 2, disclosed is a technique in which movement of impurities inside the crucible is suppressed to thereby prevent deformation of the crucible or dissolution of impurities from the inside of the crucible by intermittently supplying a voltage for testing leakage of a melt.
Further, in patent document 3, disclosed is a technique in which during the time from touch of a seed crystal at a silicon melt to at least formation of a crystal trunk portion, a voltage supplied to a pulling shaft of the seed crystal is kept at a level of −50 V to +50 V (0 V being excluded). Furthermore, in patent document 4, disclosed is a method in which an electric field, e.g., a constant electric field or a periodic pulse wave is supplied to a vitreous crucible filled with silicon melt so as to decrease or prevent deterioration of an inner surface of the quartz crucible.
Moreover, in patent document 5, disclosed is a method in which alkali metal ions are contained in a vitreous crucible and are concentrated near an inner wall surface of the vitreous crucible to efficiently devitrify the inner wall surface of the crucible by supplying a direct current voltage using an outer wall side as a positive electrode and the inner wall side as a negative electrode between the inner wall and the outer wall of the vitreous crucible. Also, in patent document 6, disclosed is a method in which the amount of alkali metal ions introduced into a silicon single crystal becomes uniform by making a current flowing through the silicon single crystal constant during pulling of the silicon single crystal.